PURPOSE: To develop an internationally standardized and validated tool to assess skill in performing tube shunt surgery. METHODS: A panel of 6 glaucoma surgeons developed a tool for assessing tube shunt surgery using a modified Dreyfus scale for skill acquisition. The tool was reviewed by a panel of 10 international content experts, and their comments were incorporated into the final rubric. A different panel of 8 international glaucoma specialists independently graded 6 surgical videos performed by surgeons at various levels of ophthalmic training to calculate inter-rater reliability for each step in the rubric. RESULTS: The tube shunt rubric contains 13 steps specific to tube shunt surgery and 7 global indices. The Cronbach's alpha statistic, a measure of internal reliability, ranged from 0.75 to 0.96, indicating strong internal reliability for all 13 steps. CONCLUSIONS: The tube shunt assessment tool has face validity, content validity, and inter-observer reliability, and can be used to assess tube shunt surgery skills. Further studies are required to determine predictive and construct validity.